The present invention relates to a radio wave transmissive cover arranged in a radio wave path of a radio wave radar device.
Millimeter wave radar devices (hereafter referred to as the radar device) have been installed in some vehicles in recent years such as automobiles in order to measure the distance or the relative speed between the vehicle and a nearby vehicle or obstacle. If the radar device in such a vehicle is arranged to be exposed, the radar device may adversely affect the design feature of the vehicle. In view of this, the radar device is arranged behind an emblem or a front grille located in the front of the vehicle, for example, and the emblem or the like is formed by a radio wave transmissive cover (hereafter referred to as the cover) through which radio waves pass (see Japanese Laid-Open Patent Publication No. 2008-230497).
The cover disclosed in the above publication includes a design layer, a cover layer for covering the front surface of the design layer, and a base material layer for covering the back surface of the design layer. The cover layer includes a first cover layer made of a first transparent plastic material and a second cover layer made of a mixed material containing the first transparent plastic material and colorant in which the second cover layer covers a part of the back surface of the first cover layer. The second cover layer includes a general part adjacent to the back surface of the first cover layer and a cover-side engaging part having an undercut shape in which the cover-side engaging part protrudes from the back surface of the general part on the entire circumference. The base material layer is made of a second plastic material having a melting point different from the melting point of the first transparent plastic material. The base material layer includes a base-material-side engaging part that is engaged with the cover-side engaging part.
With such a cover, the cover-side engaging part of the second cover layer and the base-material-side engaging part of the base material layer are engaged with each other, so that the second cover layer and the base material layer are mechanically fixed to each other. This provides firm integration of the second cover layer and the base material layer even in a case where the second cover layer and the base material layer are made of materials having melting points different from each other. As a result, the gap between the second cover layer and the base material layer is sealed, thereby preventing infiltration of water such as rainwater.
In such a cover, it is necessary to form the cover-side engaging part having the undercut shape and the base-material-side engaging part on the entire circumference in order to seal the gap between the second cover layer and the base material layer made of plastic materials having melting points different from each other. Due to this, if a camera for recording the front of the cover is to be arranged behind the cover, for example, it is necessary to form a recessed part that is recessed inwardly relative to the circumference on the outer circumference of the cover in order to make space for the camera lens. This may adversely affect the design feature of the cover.